The invention relates to a method and an arrangement for operating and monitoring an internal combustion engine.
The monitoring of the control of a conventional internal combustion engine on a torque basis is shown in DE-A 195 36 038 (U.S. Pat. No. 5,692,472). There, a maximum permissible torque or a maximum permissible power is determined at least on the basis of the accelerator pedal position. Further, the actual torque or the actual power of the internal combustion engine is computed in dependence upon the engine rpm, ignition angle position and load (air mass, et cetera). For monitoring, the maximum permissible value is compared to the computed actual value. Measures for fault reaction are initiated when the actual value exceeds the maximum permissible value. The measures for fault reaction comprise reducing power, for example, by cutting off the metering of fuel to the engine until the actual value again drops below the maximum permissible value.
This monitoring strategy affords a reliable and satisfactory monitoring of the control of the engine in the entire operating range. It is based, however, on the measured air mass supplied to the engine. For internal combustion engines, which are operated at least in one operating state with a lean air/fuel mixture, the torque, which is determined from the measured air mass, or the determined power does not correspond to the actual values so that the described monitoring can be utilized only to a limited extent.
This is so primarily for internal combustion engines having direct injection because, in stratified operation, the detected air mass and the adjusted ignition angle are not sufficient for computing the actual torque. The injected fuel mass, which cannot be measured, here has, as with all lean-operated engines, a great effect on the torque which cannot be considered by the procedure in the state of the art. However, especially the fuel mass can be too high because of the influence of defects such as a rail pressure which is too high or an injection valve which closes too slowly so that a torque, which is too high, can occur and therefore unwanted operating states of the engine can result.
It is an object of the invention to provide measures for monitoring the control of an internal combustion engine which is operated at least in some operating states with a lean air/fuel mixture.
A procedure for controlling a direct-injection gasoline internal combustion engine is disclosed in U.S. Pat. No. 6,092,507. This engine is essentially controlled in two different modes of operation, the stratified operation and the homogeneous operation. In homogeneous operation, fuel is injected during the induction phase and the engine is throttled. In stratified operation, the injection is during the compression phase and the engine is operated without throttling.
In the homogeneous operation, a desired torque value is determined from at least the position of the accelerator pedal. This desired torque value is converted into a fuel mass to be injected. Furthermore, and proceeding from this fuel mass, a desired throttle flap angle for adjusting the air supply to the engine is determined in the sense of an adjustment of a pregiven desired value for the composition of exhaust gas. The latter does not apply to the stratified operation wherein the engine is unthrottled, that is, is operated with an open throttle flap. The homogeneous operation takes place at least in the region of higher loads; whereas, the stratified operation takes place in the region of lower loads or in the part-load region. Measures for monitoring functions of the control system are not described in the above-mentioned publication.
The solution in accordance with the invention permits an effective and adequate monitoring of the control of an internal combustion engine which is operated at least in some operating states with a lean air/fuel mixture.
Special advantages are shown with the monitoring of the function of the control of internal combustion engines having gasoline-direct injection.
It is especially advantageous that, when the engine is operated with a lean mixture in dependence upon the accelerator pedal position, a maximum permissible torque is derived above which the air supply to the engine is limited. This takes place preferably by closing the throttle flap.
It is of special advantage that only for a released accelerator pedal (that is, with the pedal position in idle), a maximum rpm is pregiven above which the air supply is limited. In this way, at least an especially critical operating state is covered by a precise and reliable fault detection so that no unwanted operating situation can develop in this operating state.
In this way, it is ensured that for switched off fuel (for example, because of a leaking injection valve), an ignitable mixture is still provided and the torque or the power is not impermissibly high. In an advantageous manner, the fresh air supply is so adjusted that, if an injection would take place, a torque would result for a stoichiometric mixture composition which leads to no impermissible vehicle reaction.
Of special advantage is, as a supplement or in the alternative to the above solution, the switchover to stoichiometric or rich operation. Then access can be made to the monitoring method known from the state of the art. In an advantageous manner, this is carried out when the accelerator pedal is released. Here too, it is advantageous when the supplied fresh air quantity is so adjusted by control of the throttle flap in dependence upon the driver input and the rpm so that an idle torque results. If the instantaneously computed torque or the instantaneously computed power exceeds, then this fault is detected and countermeasures are initiated.
In an especially advantageous manner, the maximum rpm is applied for monitoring with the pedal released and the fresh air quantity is limited. Either the metering of fuel is switched off or, in special operating states, the stoichiometric operation is initiated. The operating states are those wherein, for example, a switchoff above the rpm cannot take place because of a hot catalytic converter or for reasons of comfort, for example, in first gear. In both cases, access is made to the known monitoring method based on the determined air supply.